fix(web): use natural asset order for navigation

[uhthomas]

Fixes: #3091

[vercel]

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1 Ignored Deployment

Name	Status	Preview	Comments	Updated (UTC)
immich	⬜️ Ignored (Inspect)			Jul 3, 2023 0:59am

[jrasm91]

LGTM

[brighteyed]

I haven't tested it myself yet, but looking into code it seems the issue may still exist.

_assetGridState.assets is a flattened list of all the assets for already loaded buckets. In general, buckets are loaded in "random" order if the user clicks on the scrollbar. In this case, we will find the next/prev index, but the asset for this index may not be from the adjacent bucket.

[brighteyed]

Yes, I can reproduce the bug on main (2099b04057a161ec44b557abac17763b4e696657).

Steps to reproduce:

1. Open the main timeline (the first N bucket(s) are loaded now)
2. Click on the scrollbar somewhere near the bottom (some bucket(s) near that location are loaded. Note: _assetGridState.assets now contains assets from nonadjacent buckets)
3. Click on any asset to open AssetViewer
4. Click the Previous button multiple times. When we reach the end of the bucket(s) loaded in (2), we begin to show assets from buckets loaded in (1) thus missing a lot of assets in intermediate buckets.